Carrier current communication system



P. SPORN El' AL CARRIER CURRENT CQMMUNICATION SYSTEM July 10, 1934.

2 Sheets-Sheet 1 mw, mw um,

Filed Aug. 22. 1930 July l0, 1934.

P. sPoRN Er Al.

CARRIER CURRENT COMMUNICATION SYSTEM Filed Aug. 22. 1930 2 Sheets-Sheet2 wvemtou Pff/UP .SPO/'ew /EA Y nl. WOL Fa@ 33513 MMM @Moz/nap R 1 -J-der all normal and emergency conditions.

Patented July 10, 1934 UNITED STATES CARRIER CURRENT COMMUNICATIONSYSTEM Philip Sporn, New York, N. Y., and Ray H. Wolford, Elizabeth, N.J.

Application August 22, 1930, Serial No. 476,978

5 Claims.

This invention relates to carrier current communication systems,particularly for use as communication means on electric powertransmission and distribution systems, and has among its ob- 5 jects theprovision of such communication system in which the excessive costs andhazards of the present coupling arrangements between the high frequencycommunication apparatus at the stations and the power line conductorsare reduced 1,3 and eiiicient coupling is secured with great decrease incost, increase in reliability of service, and reduction of the number ofoperating devices at the coupling stations. The foregoing and otherobjects of the inl vention will be best understood from the followingdescription of exemplications thereof, reference being had to theaccompanying drawings wherein,

Fig. l is a diagrammatic View of a portion of Z9 a power transmissionand distribution system provided with a carrier communication system inaccordance with our invention;

Fig. 2 is a diagrammatic View of a transmission line tower showing thearrangement of the trans- :j mission line conductors of the system shownin Fig. 1; and

Fig. 3 is a sectional view through'a circuit breaker unit employed atthe individual stations 'of the power system shown in Fig. l,illustrating w'the arrangement of the coupling condenser in the lead-inbushing by means of which the high frequency receiving and transmittingapparatus at the stations is coupled to the line conductors.

Experience has shown that carrier current y communication systemsoperating over power transmission and distribution lines constitute oneof the most reliable means for maintaining continuous communicationbetween the stations of a power transmission and distribution system un-One of the greatest diiiiculties in the practical application. of suchcommunication systems resides in the excessive cost of the couplingequipment by means of which the carrier frequency energy is caused toenter or leave the transmission line at the individual stations, andalso the complications involved in maintaining such coupling equipmentin proper operating condition. At present, two types of coupling meansare used. 3l One is in the form o f an antenna strung parallel to thepower line, and the other is in the form of capacitors installed asseparate and distinct units at the individual stations of the system.They are described in a paper entitled Experience 57 with CarrierCurrent Communication on a High Tension Interconnected TransmissionSystem, which we presented before the American Insttute of ElectricalEngineers in December, 1929, ,and which has been printed in thepublications toof that Institute. Experience has shown that the antennamethod of coupling is a source of many difficulties and accordingly itis now the almost uniform practice to use coupling capacitors, of whichthere are various forms now on the market. These coupling capacitors areinstalled as separate units and constitute an additional piece ofapparatus 'at the stations, requiring additional space and making itnecessary to provide proper clearances for establishing connections toysulation. Instead, we utilize for coupling purposesV the ordinaryequipment that is essential and must be provided for the operation ofthe power stations, such as circuit breakers, and combine relatively lowvoltage coupling means with the high voltage equipment of such standardoperating apparatus in a way to secure satisfactory communication,comparable with that obtained by the use of separate coupling capacitorsor antennae, in accordance with the prior practices. The details of thearrangement of our invention will be clearly understood from thefollowing description of a carrier current communication system of whicha section including stations A and B is shown in the drawings.

The power transmission system is, as usual, of the three-phase type andmay, for instance, operate on 132 KV. At each station there is provideda set of high voltage bus bars 1, 2, 3 for` the three phases of thesystem. The stations A and B are shown interlinked by two parallelthreephase circuits M and N, each circuit comprising three lineconductors 1,r 2, 3, corresponding to the three phases of the system.There are also shown at station B, two additional outgoing highvoltagetransmission line circuits O and P, each likewise including three lineconductors l, 2, 3 corresponding to the three phasesof thesystem, thecircuits O and P going to the next station of the system. From station Athere is also outgoing a single circuit transmission line Q having threeconductors 1, 2, 3 corresponding to the three phases of the system.

The power transmission lines are carried between the stations ontransmission line towers as shown in Fig. 2, which also illustrates thearrangement of the line conductors of the circuits M and N on the tower.As seen in Fig. 2, the two transmission lines are strung asymmetricallyon the tower, circuit M having phase 1 on the top, and circuit N havingphase 3 on the top. This reduces the reactance of the transmission line.

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To control the transmission of power over the circuits there areprovided at the-stations, sets of three-pole circuit breakers AM, AN,BM, BN, BO, BP and AQ, by means of which the individual lines of thetransmission circuits may be connected or disconnected from the bus bars1, 2, 3 at the stations. The individual circuit breaker sets AM, AN,etc. are all of a type well known in connection with high voltage powertransmission.

Each circuit breaker set consists of three like units 10 illustratedwith more detail in Fig. 3. Each unit comprises a large oil-filled metaltank 11 having mounted at its top two upwardly divergent lead-inbushings l2 through which extend lead-in conductors 13 terminating attheir lower ends in contact members 14. The circuit between the contactmembers is completed by a conducting bridging element 15 which is moveddown to open the circuit breaker and up to close the circuit breaker, bymeans of a rod 16 that is operated by suitable motion transmittingmechanisms 17 and actuated by an actuating device 19 that is common tothe Ythree units of a circuit breaker. Such circuit breakers with thehigh voltage lead-in bushings 12 are common and standard equipment ateach power station and must be provided whether there is a carriercommunication system used or not. The bushings must provide insulationfor the full line voltage, and one of the common types of bushings isthe so-called oil-lled bushing", as shown in the drawings. The bushingas shown comprises a cylindrical supporting collar 20 of metal which issecured at the top to the tank. Over the top and bottom of this collarare mounted porcelain shells 21 which in conjunction with the collar,form a closed hollow chamber. The lead-in conductor 13extendslongitudinally through the center of this chamber and isinsulatingly held at its endby the ends of the porcelain shells 21. Theinterior of the chamber is filled with oil, so as to provide thenecessary insulation against dischargesand break-down between thelead-in conductor 13 and the surrounding metallic portions, cylindricalbarriers 22 of impregnated paper or similar insulating material servingto strengthen the insulation.

In accordance with our invention, such high voltage lead-in bushings ofthe standard apparatus used at the stations are employed to pro- 'videthe coupling means for the carrier current communication system. To thisend, there is provided within the interior of the bushing an additionalcapacitive coupling member 23 which may be in the form of acylindrically wound plate, preferably arranged so as to have its endsout of contact. 'Ihis coupling plate 23 is insulatingly held at adistance from the walls of the collar 20 of the bushing so that theplate has a capacitive coupling with the lead-in conductor 13 and also acapacitive coupling with the collar 20 of the bushing. As a result, thecollar 20, coupling plate 23 and lead-in conductor 13 constitute twoserially arranged condensers, one condenser being formed of the lead-inconductor 13 and the coupling plate 23, and the other condenser beingformed of the coupling plate 23 and the supporting collar 20. A lead-inconnection is provided to the coupling plate 23 on the bushing by meansof a lead-in conductor 25 extending through a small bushing 26 on thecollar 20 and then pass. ing through a suitably sealed port 27 on, thetank 11 of the circuit breaker to the exterior thereof.

The details of construction of the bushings as shown in Fig. 3 do notconstitute a part of 011.1. n-

vention, and for more particulars as to their construction 'reference ishere made to Eby Patent No. 1,657,249. It is of course understood thatthe description of the particular type of bushing is intended only forillustrative purposes as our invention is in no way limited to the useof any particular type of bushing, but is broadly applicable to the useof lead-in bushings for the station apparatus such as circuit breakersor transformers having embodied therein capacitive coupling meansinsulated from the leads to the bushings but having capacitive couplingtherewith, for the purpose of coupling carrier current communicationapparatus to high voltage power lines.

The several circuit breakers shown in Fig. 1 are of the type describedabove and are provided with lead-in bushings having capacitive couplingplates 23 as indicated in the drawings.

In accordance with our invention, we employ as a means for passing thehigh frequency signal energy of the carrier communication system betweenthe line and the transmitting and receiving apparatus at the stations,the capacitive coupling plates mounted in the bushings of the circuitbreakers or like `standard station apparatus that is used in connectionwith the transmission and control of power entering and leaving thestation. .We have found that by proper arrangement standard bushings asthey are now available on the market can be used satisfactorily fortheprovision of such coupling means, and that capacitive coupling plates23 may be provided in such bushings that will permit transfer ofSunicient energy into the line conductors for maintenance of reliablecarrier communication. In a typical bushing of this type, for 132 KV,the capacity between the coupling plate 23 and the lead-in conductor 13was found to be .0002 microfarads, the capacity between the couplingplate and the supporting collar 20 amounted to .004 microfarads, and theVsystem according to our invention using such bushings for couplingpurposes was found to give satisfactory and reliable carriercommunication on an extended 132 KV power transmission system.

' The details of the arrangement of such system as practically operatedare seen in Fig. 1. operating the carrier current communication systemon the two parallel circuits M and N between the stations A and B, thecarrier current is transmitted inter-phase and inter-circuit, i. e., twophases of each circuit are used to provide a closed communicationcircuitand the two cir-v cuits are used in parallel. In the instancereferred to, phases 1 of circuits M and N are coupled in parallel to onepole of the carrier current communication apparatus and phases 3 of thecircuits M and N are coupled in parallel to the other pole of thecarrier current communication apparatus. The outgoing bushings of thecircuit breaker sets at the two stations are used for couplingpurposes,and as seen, the lead-in terminals 25 of the bushing couplingplates 23 of phase 1 of circuit M and of phase 1 of circuit N areconnected in parallel to the conductor 31,

and the lead-in terminals 25 of the couplingv plates 23 .of the outgoingbushings of phase 3 ofV line Mand of phase 3 of line N are connected inparallel to conductor 32.

These conductors have associated therewith protective apparatus in theform of spark gaps 33, and the other usual protective devices which areas a rule in the coupling circuits between the carrier currentcommunicationA apparatus and the transmission line. The conductors 31and 32 lead to a tuning unit comprising variable inductances 34 and 35and condensers 36, the circuit being completed by a coupling inductance3'7, to which in turn are connected the leads 38 from the carrierfrequency transmitting and receiving apparatus indicated in the drawingsby a rectangle 39.

The details of construction of the transmitting and receiving apparatusand of the tuning unit do not constitute a part of the present inventionand may be of the type heretofore used in carrier currentsystems'utilizing antenna wire or separate capacitive coupling. A fullerdescription of such tuning and transformer and receiver apparatus willbe found in our paper on carrier current communication referred tohereinbefore.

In the station B of the system, the coupling plates in the outgoingbushings of the circuit breakers BM, BN, BO and BP of the two circuits Mand O are connected pairwise to two coupling coils 37 in a similarmanner asy in Station A, and as shown in the drawings, the two couplingcoils are interconnected in parallel by means of coupling conductors 45,46 to which in turn are connected the leads from the transmitting andreceiving apparatus 39. Because of this arrangement, the circuits M andN will constitute a continuous communication line with the circuits Oand P, so as to permit direct communication between station A and thestations on the circuits O and P. The tuning apparatus connected withthe coupling plates of the bushings of the circuit breakers BM, BN, BOand BP, when properly adjusted, constitute thus in conjunction with theconductors 45, 46, a resonant by-passing circuit by means of whichcarrier current power is free to iiow between the circuits M-N and O-P,even when the bridging contacts in any of the breakers BM, BN, BO and BPare open. The provision of the by-passing circuit is desirable onstations in which Vcircuit breakers or other power apparatus havinglead-in bushings provided with coupling plates as explained before areinstalled and connected to the high voltage power lines, regardless ofwhether or not carrier current communication transmitting and receivingapparatus is provided at the station. In this way, it is possible toprovide a very positive communication tie between all the lines andcircuits of the system by merely providing connections between thebushing taps, as explained.

l'Ehe usual frequencies used at present in 0perating carrier currentcommunication systems on power lines lie within the range of about 50kilocycles to about 150 kilocycles. In general, the higher thefrequency, the easier it is to transfer the amount of power required toestablish reliable communication through a given capacitor coupling. Wehave found that a system arranged as described in connection with Fig. 1operated in a reliable and satisfactory way at frequencies as low as 49kilocycles.

A particular feature of our invention is the utilization of combinedinterphase and intercircuit transmission of carrier frequency currentsover parallel transmission line circuits. Heretofore, wherever carrierfrequency communication was used between remote stations, there wasemployed either interphase of intercircuit carrier communication. In theinterphase carrier communication, one conductor of the carrier frequencyapparatus cuit. In the intercircuit system, which is usable where thereare two independent circuits extending between the communicatingstations of the system, euch as is now common practice, one conductor ofthe carrier frequency apparatus at each station was coupled to one phaseof one circuit andthe other conductor to another phase of the othercircuit. By combining the interphase and intercircuit coupling of thetransmitting and receiving apparatus at the communieating stations withthe utilization of the coupling plates in the bushings of the outgoingcircuit breakers, We greatly increase the reliability of thecommunication system and at the same time enable efcient carrierintercoinmunication through the capacitive coupling of the condenserbushings already present in the station under elimination of additionalcostly capacitors.

The combined interphase and intercircuit coupling as used between thestations A and B of the arrangement shownin Fig. 1 is of course possibleonly where two circuits extend between the sta# tions. However, thebroad principles of the invention vinvolving the utilization ofcapacitive coupling plates in the bushings of circuit breakers andsimilar standard power apparatus at the stations are not limited to theuse in double circuit sections of the line, but are likewise applicableto single circuit line sections. Such arrangement is shown in connectionwith the line section Q extending from station A of the system, wherethe coupling capacitor plates of the circuit breaker bushings, on theline-side as well as on the station-side, on phases 1 and 3 of circuit Qalone are connected to the two conductors 31 and 32 leading to thetransmitting and receiving apparatus in a manner similar to the Way theequipment on the circuits M and N is connected interphase-intercircuittothe communication apparatus.

In order to secure maximum transmission of the high frequency carriercurrents it is important to prevent loss of high frequency power by wayof the condenser formed by the coupling' cuit having a very highimpedance at the carrierl frequency used, and te act as an anti-resonantelement and cause substantially most of the carrier frequency current toflow into the line conductor over which communication is desired. In

accordance with our invention, we. so design or tune the inductancecoils 34 connected to the'I conductors 31 and 32 leading from thecoupling plates 23 as to make the impedance to the flow:

of carrier frequency currents to the ground relatively large, thussecuring a high degree ofv cinciency of transmission and utilization ofthe. capacity coupling between the coupling plates 23 and the lead-inconductors 13 in the bushigs.

The anti-resonant coils 34 may also beV used' fcr drainage, or separatedrainage coils may be provided.

Although practical limitations may sometimes prevent the securing of anextremely high antiresonant impedance, nevertheless it is possible tosecure an impedance value suiiiciently high to' prevent the loss ofexcessive carrier frequency I power through the condenser formed by thecoupling plates in the bushingand the grounded metal parts of thecircuit breakers.

By combining suitable capacity and inductance elements with the capacityelements formed by the coupling plates 23 and the metal collars 20 orother grounded metal parts of the bushings or circuit breakers,electric' wave lters of the band and high-pass types are secured whichwave lters are useful in controlling the frequency band of carrierfrequency energy passing from the carri-er frequency transmittingapparatus to the power conductors and from the power conductors to thecarrier frequency receiving apparatus. According to our invention, weemploy the capacity elements formed by the coupling plates 23 and themetal collars 20 as part of .the capacity elements of such electric wavefilters.

It is of course understood that the apparatus andthe system of ourinvention are provided with all the devices and Xtu'res usually enteringinto a power station, such as transformers, lightning arresters,disconnecting switches, metering equipment, etc., but we have omittedthese devicesfrom the description of the exemplication of theinventionfor the sake of clearness.

Instead of using the lead-in bushings of the circuit breakers at thepower stations, the lead-in conductors of other pieces of apparatus usedat the stations may be employed for establishing the couplingconnections with thetransmission line, inaccordance with the principlesof our invention, avoiding the installation of separate devices forcoupling apparatus and the expense of and diiioulties incidentalthereto.

v rInstead of using only the lead-in bushings on theA outgoing sides ofthe circuit breakers for coupling of the carrier current apparatus withthe transmission lines, it is of advantage to use in addition thebushings on the bus-bar side of the circuit breakers for coupling withthe carrier current apparatus. To this end, the conductors 31 and 32leading from the coupling plates 23 oi the 'circuit breaker bushings asshown in Fig. 1 are extended and connected also to the coupling plates23 on the bus-bar sides of the individual circuit breakers, thusconnecting the coupling plates on both the outgoing and incoming sidesof the breakers in parallel. The capacity coupling between the carrierfrequency equipment and the lines is thus doubled, but this doubledcapacity is fully eiective only when the circuit breakers are closed.Such arrangement is shown in connection with the circuit breakers AQ onthe circuit Q outgoing from station A, and the circuit breakers BO, BP,on the outgoing circuits O and P of station B. As arule, where parallelcircuits are used, at least one set of circuit vbreakers is closed at atime so that the advantage of the increased coupling between the highfrequency carrier equipment and the transmission lines is made use ofpractically all the time. n

`Furthermore, as an alternative, the coupling plates of the bushings onthe outgoing side of the breakers may be connected to a tuning unit andthe coupling plates on the incoming side of the breakers may likewise beconnected to a separate tuning unit.

The invention is not limited to the particular details of constructionor arrangements or method of operation described for purposes of eX-emplication hereinabove, but is susceptible of many other embodimentswhich will suggest themselves to those skilled in the art. It is ac- 4cordingly desired that the appended claims be given a broadinterpretation commensurate with the scope of the invention within theart.

We claim:

1. Ina carrier current communication system for high voltage powertransmission systems, a plurality ofremotely located power stations, apair of polyphase power transmission circuits extending between saidpower stations, each circuit comprising a set of polyphase high voltageline conductors, power apparatus at said stations controlling the flowof high voltage power' through said line conductors, high voltagelead-in bushings on said apparatus for effecting connection of theoperative parts of said apparatus to said high voltage line conductors,carrier frequency communication apparatus at the stations having twopole terminals, coupling condenser means in two bushings of one phase inthe two circuits connected to one terminal of said communicationapparatus, and'coupling condenser means in two bushings of another phasein the two circuits connected to the other terminal-of saidcommunication apparatus to effect carrier frequency communicationbetween said-stations over said phase conductors.

2. In a carrier current communication system for a high voltage powertransmission system, a plurality of remotely located power stations, apair of polyphase power circuits extending between said stations, eachpower circuit comprising a set of three-phase high voltage lineconductors, means for supporting said line conductors in insulatedrelationship along each other, power apparatus at said stations, saidpower apparatus including circuit breaker units for the individuallines, each circuit breaker unit comprising high voltage lead-inbushings, said lead-in bushingsv having a high voltage lead-in conductorconnected to the high voltage line and an insulating enclosure formaintaining said lead-in conductors in insulated condition, carrierfrequency communication apparatus at said stations Yhaving two' lll-5closures constituting condensers in conjunction with the lead-inconductors extending through the bushings, connections from the couplingmembers in two bushings of one phase in the two circuits to one terminalof said communication apparatus, and connections from the couplingmembers in two bushings of another phase inthe two circuits connected tothe other terminal of said communication apparatus to effect carrierfrequency communication between said stations over said phaseconductors.

3. In a carrier current communication system for a high voltage powertransmission system, a plurality of remotely located power stations, apair of polyphase power circuits extending between said stations, eachpower circuit comprising a set of polyphase high voltage lineconductors, means for supporting said line conductors in insulatedrelationship along each other, power apparatus at said stations, saidpower apparatus including circuit breaker units for the individual lineconductors, each circuit breaker unit comprising a high voltage lead-inbushing on the lineside and a high voltage lead-in bushing onapparatus-side of the station, said lead-in bushings having a highvoltage lead-in conductor connected to the high voltage line and aninsulating enclosure for maintaining said lead-in conductors ininsulated condition, carrier frequency apparatus at said stations havingtwo pole terminals,

low potential within said bushing enclosures constituting condensers inconjunction with the leadin conductors extending through the bushings,connections from one terminal of said communication apparatus to thecoupling members in the line-side and station-side bushings of twocircuit breaker units of one phase in the two circuits, and connectionsfrom the other terminal of said communication apparatus to the couplingmembers in the line-side and station-side bushings of two circuitbreakers of another phase in the two circuits to eiect carrier frequencycommunication between said stations over said phase conductors.

4. In a carrier current communication system for a high voltage powertransmission system, two remotely located power stations, a powercircuit section extending between said stations comprising a pluralityof line conductors of different high voltages, means for supporting saidline conductors in insulated relationship along each other, powerapparatus at each station including a set of bus-bars of differentvoltages corresponding to said lines and circuit breaker units forconnecting and disconnecting the individual line conductors to thecorresponding bus-bar at the station, each circuit breaker unit having ahigh voltage lead-in bushing on the line-side and a high voltage lead-inbushing on the bus-bar side, carrier frequency communication apparatusat each of said two stations coupled at the opposite section ends to oneof said line conductors acting as carrier conductor maintaining carriercommunication between said two stations, and a pair of couplingcondensers in the line and busbar bushings of the circuit breaker unitof said carrier line conductor at one of said stations coupling throughsaid two bushing condenser paths in parallel one terminal of the carriercommunication apparatus at said station to said carrier line conductorto carry thereover carrier frequency currents between the communicationapparatus at said one station and said second station.

5. In a carrier current communication system for a high voltage powertransmission system, two remotely located power stations, a powercircuit section extending between said stations comprising a pluralityof line conductors of diierent high voltages, means for supporting saidline conductors in insulated relationship` along each other, powerapparatus at each of said two stations controlling the flow of highvoltage power through said line conductors, high voltage lead-inbushings for effecting connection of the ends of said line conductors tothe operative parts of the associated apparatus, carrier frequencycommunication apparatus at each of said two stations coupled to oppositesection end portions of two of said line conductors acting as parallelcarrier conductors maintaining carrier communication between said twostations, and a coupling condenser in the lead-in bushing of each ofsaid two carrier line conductors at one c1" said stations coupling eachof said two carrier line conductors to one terminal of the carriercommunication apparatus at said station to carry through the parallelbushing condenser paths of the two bushings at said station, and the twocarrier line conductors leading to the second station carrier frequencycurrents between the communication apparatus of said two stations.

PHILIP SPORN. RAY H. WOLFORD.

